An AC LED driving circuit proposed as a scheme for driving an LED under an AC power condition is advantageous in that a manufacturing process is simple, a defect rate is low, and a lifespan is long, compared to a Switched Mode Power Supply (SMPS) scheme.
Referring to FIG. 1, FIG. 1 is a diagram showing a conventional, typical AC LED driving circuit. Such an AC LED driving circuit has sequential control of current sources as a fundamental principle.
However, such an AC LED driving circuit has great vulnerability from the standpoint of occurrence of flicker due to a fundamental driving scheme in spite of excellent advantages such as high efficiency, long lifespan, and high reliability, and reduction in the size of LED lighting compared to an SMPS-type LED lighting driver. That is, the AC LED driving circuit basically adopts a scheme for sequentially driving current for a varying input voltage, thus making it very difficult to be completely free from LED shading.
Referring to FIG. 2, FIG. 2(a) shows an image acquired by capturing a commercial lighting device in which an actual AC LED driving circuit is used. As shown in FIG. 2(b), when power is driven at a frequency of 60 Hz, and the periodic turning-on/off operations of LEDs occur at a frequency of 120 Hz. Typically, since a person cannot perceive regular flickering of light occurring at a frequency of 80 Hz or more, there is no problem with the naked eye. However, when a light source, operating as shown in FIG. 2(b), is directly captured, regular black stripes appear horizontally or vertically in a picture and a video, as shown in FIG. 2(a). A phenomenon in which such a regular black stripe appears is called a stroboscopic effect.